Jason Jay Jaynes went to trial Thursday on charges he had sex with underage girls. He also faces trial next year on a murder conspiracy charge.

The two cases unexpectedly merged during testimony from one of Jaynesâ alleged victims.

The witness, now 26 and an inmate at Coffee Creek Correctional Institution, said she had sex with Jaynes when she was 12 and he was 19.

She also disclosed that Jaynesâ mother, Susan Ellen Campbell, pressured her not to testify at his trial.

Jaynes and Campbell, also a Coffee Creek inmate, were charged in the 2011 murder of Deborah Higbee Benton. Campbell, who was convicted for her role in the murder, has agreed to testify against Jaynes and former police detective Lynn Edward Benton, the dead womanâs husband.

Benton is tied to the sex case as well. He allegedly ignored reports about Jaynes' involvement with underage girls in 1999 and derailed the investigation, according to a tort claim filed against Gladstone last year.

It is unclear whether Campbell influenced the witness, but the womanâs story on the stand was radically different than the one she initially gave to investigators and confirmed for the prosecution on Wednesday, said Clackamas County Senior Deputy District Attorney John Wentworth.

Jaynes faces numerous rape, sodomy and sex-abuse charges that stem from two incidents.

The incidents happened at least 14 years ago, and the recollections of the alleged victims and an eyewitness were cloudy at best.

But they told generally consistent stories.

On March 22, 2000, three unrelated girls who were living at a Northeast Portland foster home contacted Jaynes, who took them to a house in Gladstone. There Jaynes and another man had sex with two of the girls.

Their stories diverged. The witnesses differed on who called Jaynes, how many people were in the car, how many people were at the house.

But they all agreed that Jaynes was there and two of the witnesses said they had sex with Jaynes.

The two girls who said they had sex with Jaynes had been drinking heavily.

âWe were wasted,â one of them said.

âI have chunks of memory of (the night),â said the other. âIt was very long ago.â

Jaynes and another man exchanged high fives after having sex with the girls, said a witness who was at the house.

Wentworth offered a corroborating witness, Craig Smith, who got to know Jaynes while serving two weeks in the Clackamas County Jail.

Smith said Jaynes admitted having sex with the girls and mentioned the high-five hand slap.

Other of the sex charges involves a former neighbor.

She said she met Jaynes when she was 5 and he was 8 and that they started engaging in sexual activities when she was in eighth grade.

"I lost my virginity to him the summer going into my sophomore year," she said. She was 15 and he was 18.